Hypodermic needles are widely used in the biomedical field for injection into and extraction from living tissue. Hypodermic needles generally have a relatively large diameter, for example on the order of millimeters. Unfortunately, the large diameter can damage biological tissue during penetration. Moreover, tissue penetration often is painful due to the relatively large needle diameter.
Accordingly, microneedles are being developed, that can have diameters that are on the order of microns. The smaller diameter needle can reduce damage to living tissue and/or reduce pain. More precise injection and extraction also may be provided. In order to inject or extract a requisite amount of liquid through a microneedle of relatively small diameter, an array of microneedles, often referred to as a microneedle array, generally is provided. For example, a microneedle array may have dimensions on the order of 1 cm2 and may include tens, hundreds or even thousands of microneedles thereon. Microneedles are described in U.S. Pat. No. 5,457,041 to Ginaven et al. entitled Needle Array and Method of Introducing Biological Substances Into Living Cells Using the Needle Array; U.S. Pat. No. 5,658,515 to Lee et al. entitled Polymer Micromold and Fabrication Process; U.S. Pat. No. 5,591,139 to Lin et al. entitled IC-Processed Microneedles; and U.S. Pat. No. 5,928,207 to Pisano et al. entitled Microneedle With Isotropically Etched Tip, and Method of Fabricating Such a Device.
Microneedles may be fabricated using micromachining or other processes that are used to form microelectromechanical systems (MEMS). These fabrication steps may be similar to those that are used for fabricating integrated circuit microelectronic devices and thereby may be capable of relatively low-cost fabrication in large numbers. Unfortunately, notwithstanding the applicability of microelectronic fabrication techniques to the fabrication of microneedle arrays, there continues to be a need to provide improved fabrication processes for microneedle arrays that can produce microneedle arrays at very low cost, for example, less than one dollar per microneedle array and preferably less than one cent per microneedle array.